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CVE Record

CVE-2026-2758: Use-after-free in the JavaScript: GC component

Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-2758 is a critical Mozilla memory-safety flaw in JavaScript garbage collection. If systems run unfixed Firefox, Firefox ESR, or Thunderbird versions, compromise could affect data confidentiality, integrity, and availability. Mozilla says it is fixed in Firefox 148, ESR 115.33, ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Executive priority

Treat this as urgent patching work for browser and mail-client fleets. No active exploitation is confirmed in the provided sources, but the severity and memory-safety impact justify accelerated remediation.

Technical view

The issue is a CWE-416 use-after-free in Mozilla’s JavaScript GC component. The supplied CVSS 3.1 score is 9.8 with network attack vector, low complexity, no privileges, and no user interaction. Public details in the bundle do not describe exploit mechanics, root cause depth, or proof-of-concept status.

Likely exposure

Exposure is likely wherever Firefox, Firefox ESR, or Thunderbird are deployed below the fixed releases named by Mozilla. Red Hat advisories indicate downstream packaged Mozilla components may also require vendor-provided updates.

Exploitation context

The bundle does not show CISA KEV listing or another cited source confirming active exploitation. Treat exploit status as unconfirmed, while prioritizing remediation because the flaw is critical and memory-corruption class.

Researcher notes

Public source details are limited to component, CWE, CVSS, affected product family, and fixed releases. Avoid inferring exploitability beyond the CVSS vector and vendor advisories. Bugzilla and vendor errata should be monitored for clarifications.

Mitigation direction

  • Update Firefox to 148 or the applicable fixed ESR release.
  • Update Thunderbird to 148 or 140.8 where used.
  • Apply relevant Red Hat security advisories for packaged Mozilla software.
  • Check Mozilla and OS vendor guidance for any environment-specific mitigations.
  • Prioritize internet-facing, high-risk user groups and managed desktop fleets.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm deployed versions meet or exceed Mozilla’s fixed releases.
  • Check Red Hat errata applicability for managed Linux systems.
  • Review vulnerability scanner results against CVE-2026-2758.
  • Document exceptions where updates cannot be immediately applied.
Prepared
Confidence
high
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-416: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-2758 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
35Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H1.65.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2026-2758Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPfirefox: thunderbird: Use-after-free in the JavaScript: GC component
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:05:22.802Z: Reported to Red Hat.
  • 2026-02-24T13:32:58.501Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox115.33, 140.8, 148Listed
MozillaThunderbird140.8, 148Listed
Weakness

CWE details

CWE-416

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs